KVM: x86: allow setting identity map addr with no vcpus only

Changing it afterwards doesn't make too much sense and will only result
in inconsistencies.

Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 22bc5a0..dd2dd96 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1131,6 +1131,7 @@
 because of a quirk in the virtualization implementation (see the internals
 documentation when it pops into existence).
 
+Fails if any VCPU has already been created.
 
 4.41 KVM_SET_BOOT_CPU_ID